The invention relates generally to semiconductor device fabrication and, in particular, to bipolar junction transistors, fabrication methods for a bipolar junction transistor, and design structures for a bipolar junction transistor.
Bipolar junction transistors are typically found in demanding types of integrated circuits, especially integrated circuits for high-frequency applications. One application for bipolar junction transistors is in radiofrequency integrated circuits (RFICs), which are used in wireless communications systems, power amplifiers in cellular telephones, and other types of high speed integrated circuits. Bipolar junction transistors may also be combined with complementary metal-oxide-semiconductor (CMOS) field effect transistors in bipolar complementary metal-oxide-semiconductor (BiCMOS) integrated circuits, which take advantage of the positive characteristics of both transistor types in the construction of the integrated circuit.
Conventional bipolar junction transistors are three-terminal electronic devices that include three semiconductor regions, namely the emitter, base, and collector regions. Generally, a bipolar junction transistor includes a pair of p-n junctions, namely a collector-base junction and an emitter-base junction. A heterojunction bipolar junction transistor is a device type that employs at least two semiconductor materials characterized by different band gaps for the emitter and base regions, thereby creating a heterojunction. For example, the emitter of the heterojunction bipolar junction transistor may be comprised of silicon and the base of a heterojunction bipolar junction transistor may be comprised of silicon germanium, which possesses a narrower band gap than silicon.
Improved device structures, fabrication methods, and design structures are needed for bipolar junction transistors.